EDK: Some more scoped_ptr -> std::unique_ptr conversions.

After this, the remaining conversions in //mojo/edk/system are all for
scoped_ptr<MessageInTransit> (I think), and there are (semi)public API changes
in //mojo/edk/embedder.

R=vardhan@google.com

Review URL: https://codereview.chromium.org/1350503005 .
diff --git a/mojo/edk/system/raw_channel.h b/mojo/edk/system/raw_channel.h
index 9ccf280..0d5b671 100644
--- a/mojo/edk/system/raw_channel.h
+++ b/mojo/edk/system/raw_channel.h
@@ -86,7 +86,8 @@
   // Static factory method. |handle| should be a handle to a
   // (platform-appropriate) bidirectional communication channel (e.g., a socket
   // on POSIX, a named pipe on Windows).
-  static scoped_ptr<RawChannel> Create(embedder::ScopedPlatformHandle handle);
+  static std::unique_ptr<RawChannel> Create(
+      embedder::ScopedPlatformHandle handle);
 
   // This must be called (on an I/O thread) before this object is used. Does
   // *not* take ownership of |delegate|. Both the I/O thread and |delegate| must